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Calculating Ion Concentration from pH

She’s a 10?. Calculating Ion Concentration from pH. Must be on the pH scale cuz she’s pretty basic. Calculating [Ion] from pH. We use logarithms to do this N = 10 x , then log N = x [H + ] = 10 -pH [OH - ] = 10 -pOH [H + ] = invlog(-pH) [OH - ] = invlog(-pOH)

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Calculating Ion Concentration from pH

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  1. She’s a 10? Calculating Ion Concentration from pH Must be on the pH scale cuz she’s pretty basic

  2. Calculating [Ion] from pH • We use logarithms to do this • N = 10x, then log N = x • [H+] = 10-pH [OH-] = 10-pOH • [H+] = invlog(-pH) [OH-] = invlog(-pOH) • On the calculator press 2nd log-pH#

  3. Ex 1: What are [H+] and [OH-] in a healthy person’s blood that has a pH = 7.40 at temp 298 K? Kw = [H+] x [OH-] 1 x 10-14 = 10-7.40 x [OH-] 10-7.40 10-7.40 2.51 x 10 -7 = [OH-] [H+] = 10-pH [H+] = 10-7.40 M OR: [H+] = 10-pH [H+] = 10-7.40 M pH + pOH = 14 pOH = 14 - 7.40 = 6.60 [OH-] = 10-6.60 M

  4. Ex 2: What are [H+] and [OH-] at a pH = 2.3? Kw = [H+] x [OH-] 1 x 10-14 = 10-2.3 x [OH-] 10-2.3 10-2.3 2.0 x 10 -12 = [OH-] [H+] = 10-pH [H+] = 10-2.3 M OR: [H+] = 10-pH [H+] = 10-2.3 M pH + pOH = 14 pOH = 14 – 2.3 = 11.7 [OH-] = 10-11.7 M

  5. Ex 3: What are [H+] and [OH-] at a pH = 5.54? Kw = [H+] x [OH-] 1 x 10-14 = 10-5.54 x [OH-] 10-5.54 10-5.54 2.88 x 10 -6 = [OH-] [H+] = 10-pH [H+] = 10-5.54 OR: [H+] = 10-pH [H+] = 10-5.54 M pH + pOH = 14 pOH = 14 – 5.54 = 8.46 [OH-] = 10-8.46 M

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